The Mumbai Police on Wednesday warned the twin blasts, caused by RDX, that killed 52 people and injured over 100 indicated an increased level of sophistication by the terrorists.

Till date, no one has been arrested but the police are on the lookout for two men and a woman who had hired one of the taxis that was blown up.

Joint Commissioner of Police (Crime) Dr Satyapal Singh said the blasts in Ghatkopar, Jogeshwari and Mulund involved chemicals that are available locally such as ammonium nitrate, sulphates, and gelatin.

"RDX is not made in India and means it has come from abroad," he said.

Singh did not rule out the use of RDX leftover from the March 12, 1993 bomb blasts. It is believed that of the over hundreds of kilogrammes of RDX smuggled into Mumbai, some of it was not used. "That is a possibility," he admitted.

He refused to acknowledge police and intelligence failure in preventing the blasts. "Any claim that the police and intelligence were not coordinating their activities is a blatant lie," he said.

August is a season of festivals and the police are on high alert. On August 12 was Raksha Bandhan, followed by Independence Day on August 15 and Gokulastami on August 20. Ganesh Chaturthi, Mumbai's biggest festival, kicks off on August 31. But Singh insisted the police alone could not be held responsible.

"Every day, 5.8 million people use the trains and 4.6 million use the buses in this city. Moreover, every day 1000 people enter this city with the intention of staying here. How can the [40,000 strong Mumbai] police monitor each and every one of them?" he asked.

The joint commissioner of police warned that further blasts could not be ruled out and urged the citizens to be alert. "Unless we all are vigilant and careful, anything can happen. You cannot only hold the police responsible every time a blast occurs. It is humanly impossible to keep track of each and every citizen. The only way further blasts can be ruled out is through public awareness. The citizens have to play a role," he stressed.

He added that the scores of Ganeshotsav Sarvajanik Samitis [Ganesh Festival Public Committees], who erect stages across Mumbai and where Ganesh idols are placed for worship during the 10-day long festival, have been asked to stay extremely vigilant for any terrorist activity.

Clearly, the police are worried about the use of RDX, a malleable explosive with high intensity. Three forensic teams are analyzing the blast material -- the state Forensic Laboratory, Mumbai; the Central Forensic Science Laboratory, Chandigarh and the Post-Blast Investigation Team of the National Security Guards, New Delhi.

When the blasts occurred, the administration was quick to blame the Lashkar-e-Tayiba and banned Students Islamic Movement of India. Later, the state government also named the Jaish-e-Mohammad and the Pakistani Inter-Services Intelligence.

Singh insisted the police had good reason for picking the names. "Our intelligence tells us that of the 13 Islamic jihadi organisations that form a front under Osama bin Laden, the Lashkar, with headquarters in Saudi Arabia and Pakistan, is active in Mumbai and southern India, while the others are active elsewhere," he said.

"The twin blasts were well-planned and perfectly timed. Only highly trained persons could have carried it out," he added.

Singh said the police are investigating whether some Bangladeshi cells of the ISI in Mumbai were involved in the blasts, as claimed in some news reports.

The police are also looking into the involvement of women in such crimes. This is the second instance of a woman apparently being involved; the first was at the blast in Ghatkopar, northeastern Mumbai, in July last. At that time, a couple had placed a bag containing explosives under the seat of a bus. The resultant blast killed four.